In connection with the environmental requirements, which are tightened up time and time again, it has become necessary to develop improved burners and burner systems in order to comply with these requirements. The NOx-emissions (substantially nitrogen-oxides) of the burner installation is of great importance herewith, since NOx contributes to the acidification of the environment. Lowering the NOx-content of the flue gasses can be attained by using premixed burners and by supplying additional combustion air and/or recirculating flue gases to the burner. As a result, the flame temperature becomes more uniform and at the same time lower and less NOx is formed. Metal or ceramic objects are also used and are disposed in the flame. These objects radiate the heat from the flame to colder surfaces and through conduction they make the flame temperature more uniform.
A general drawback of the present gas burners which premixed combustion air and gas is the relatively low maximum load or capacity per surface unit of the burner body, thus the object, from which the mixture of gas and air flows.
In the present gas burners with a low NOx-content in the combustion gases and which comprise premixing, the burner head comprises a porous ceramic plate or a ceramic plate with bores or a heat-resisting fibrous plate or a porous metal plate, which is made of metal wires and/or fibres or of electrolytically produced porous material. Each of these embodiments has its own drawbacks: the ceramic plates are fragile, the fibre plates are mechanically not strong either, and the porous metal plates consist of wires and/or metal fibres which become too hot with certain loads, because they cannot radiate their heat to the cold material behind them.